1. Field of the Invention
The present invention relates generally to needle bearings, and more particularly to a self-contained drawn shell needle bearing having means for axially locating the bearing housing with respect to a shaft.
2. Description of the Prior Art
Prior art needle bearings are typically manufactured and sold without inner races. U.S. Pat. Nos. 4,565,458, 3,257,869, 3,248,155 and 2,488,848 are exemplary of this type construction. The needle and cage assembly is retained in an outer race which may be inserted on a hardened shaft or, in applications where an annealed shaft is used, on a separate inner race which is press fit on the shaft.
While needle bearings are designed to carry radial loads, separate means usually must be provided to carry axial loads and to axially position the needle bearing with respect to the shaft. This is typically accomplished in the prior art by providing a ball or roller bearing--which, because of its relatively deep grooves, can take some degree of axial loading--on the end of the shaft opposite from the needle bearing, or a snap ring mounted in a groove on the shaft which abuts against a shoulder on the shaft housing.
Certain kinds of unitary, self-locating needle bearings are, however, known in the prior art which do not require auxiliary means for axial positioning with respect to the shaft. U.S. Pat. No. 3,328,097 to Wilson, for example, discloses a bearing construction having a "double shouldered" inner and outer race. However, because the races are machined from relatively heavy gauge stock, the needles must be inserted by eccentric alignment of the races, as seen in FIG. 4. This is similar to the manner in which ball bearings are assembled. It should be apparent, of course, that such a method of assembly does not permit the use of a full complement of rollers.
French Pat. Nos. 2,056,710, 2,349,061 and 2,528,922 disclose various types of self-contained needle bearings made from relatively thin sheet stock. Consequently, the bearings may be manufactured with a full complement of needles by flanging the outer race over the needles during assembly. However, each of those bearings includes separate retaining elements, such as washers or rings, for locating the bearing with respect to the shaft, and are thus complex and expensive to manufacture and install.
Drawn shell needle bearings are made from strip steel stock, from which disks are blanked. The disk is progressively drawn into a cup shape by means of a series of punches and dies, and a small circle of material is removed from the bottom of the cup to form a shell for an open-ended bearing. This shell is then heat treated, the needle and cage assembly are inserted, and a finish flange is rolled into the shell to retain the cage and roller assembly.
In application, drawn shell needle bearings are pressed into their housings, with the shaft operating in a small clearance condition. Distinct from true precision bearings, there is no machining of metal on the raceway (the shell). Such bearings are relatively low cost items, giving medium precision with high radial load capacity, despite very small radial section height.
As discussed above, such bearings can bear radial load only. The shaft is free to move axially through the bearing. Generally, in order to axially locate or retain the shaft with respect to the bearing housing, a thrust bearing configuration, an angular contact ball bearing configuration, or a ball bearing must be incorporated.